Association between PD-L1 expression in monocytes and treatment outcomes in active pulmonary tuberculosis- human and animal model

Abstract

Purpose: This study aims to identify the role of PD-1/PD-L1 pathway activation in determining clinical characteristics and treatment outcomes in pulmonary tuberculosis.

Methods: We prospectively enrolled PTB, LTBI, and non-TB, non-LTBI subjects. Expression of PD-1 and PD-L1 on T cells and on PBMCs was measured. Immunohistochemistry and immunofluorescence were used to visualize PD-1- and PD-L1-expressing cells in lung tissues. The findings in humans were verified in THP-1 monocyte cell lines and mouse macrophages with Mycobacterium tuberculosis (MTB) related stimulation.

Results: A total of 76 PTB, 40 LTBI, and 28 non-TB, non-LTBI subjects were enrolled. The expression of PD-1 on CD4+ T cells and PD-L1 on CD14+ monocytes was significantly higher in PTB cases than non-TB subjects. PTB patients with positive smear and sputum smear/culture unconversion at 1 and 2 months displayed higher PD-L1 expression on monocytes before treatment initiation. IHC analysis demonstrated abundant PD-L1-expressing macrophages in lung tissues from PTB patients. In vitro MTB whole cell lysate/EsxA stimulation of THP-1 cells and mouse macrophages demonstrated increased PD-L1 expression, which can be down-regulated by co-treatment of NF-kB pathway inhibitor. IF analysis demonstrated co-localization of PD-L1 and macrophages were identified in lung tissues from mice with intratracheal injection of heat-killed MTB.

Conclusions: Increased expression of PD-L1 on monocytes in PTB patients correlated with bacterial burden and treatment outcomes. Cell and mice models confirm that MTB-related stimulation increased PD-L1 expression in macrophages.